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| author | Alan Stern <stern@rowland.harvard.edu> | 2011-09-14 12:33:16 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-09-18 01:48:37 -0700 |
| commit | 25aa55488c3644b19e33ba79c564191b8e33f477 (patch) | |
| tree | 13a18f3e4a4b20791e4d8db29789a797e4b3559e | |
| parent | 073b85469308b41468149f4aa7144c1e1bf4f0d7 (diff) | |
USB: document ehci-hcd's "companion" sysfs attribute
This patch (as1484) adds documentation for ehci-hcd's "companion"
sysfs attribute, which was added to the kernel over four years ago but
never documented.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -rw-r--r-- | Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd new file mode 100644 index 000000000000..60c60fa624b2 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd @@ -0,0 +1,46 @@ +What: /sys/bus/pci/drivers/ehci_hcd/.../companion + /sys/bus/usb/devices/usbN/../companion +Date: January 2007 +KernelVersion: 2.6.21 +Contact: Alan Stern <stern@rowland.harvard.edu> +Description: + PCI-based EHCI USB controllers (i.e., high-speed USB-2.0 + controllers) are often implemented along with a set of + "companion" full/low-speed USB-1.1 controllers. When a + high-speed device is plugged in, the connection is routed + to the EHCI controller; when a full- or low-speed device + is plugged in, the connection is routed to the companion + controller. + + Sometimes you want to force a high-speed device to connect + at full speed, which can be accomplished by forcing the + connection to be routed to the companion controller. + That's what this file does. Writing a port number to the + file causes connections on that port to be routed to the + companion controller, and writing the negative of a port + number returns the port to normal operation. + + For example: To force the high-speed device attached to + port 4 on bus 2 to run at full speed: + + echo 4 >/sys/bus/usb/devices/usb2/../companion + + To return the port to high-speed operation: + + echo -4 >/sys/bus/usb/devices/usb2/../companion + + Reading the file gives the list of ports currently forced + to the companion controller. + + Note: Some EHCI controllers do not have companions; they + may contain an internal "transaction translator" or they + may be attached directly to a "rate-matching hub". This + mechanism will not work with such controllers. Also, it + cannot be used to force a port on a high-speed hub to + connect at full speed. + + Note: When this file was first added, it appeared in a + different sysfs directory. The location given above is + correct for 2.6.35 (and probably several earlier kernel + versions as well). + |